Override "Email a Page link" in ribbon button functionality in SharePoint 2013

Hi,

I want to override "Email a Page link" ribbon button functionality on the ribbon control.

  <CustomAction Id="Ribbon.WikiPageTab.Share.EmailPageLink"
                Location="CommandUI.Ribbon"                
                Title="Custom Email this page">
    <CommandUIExtension>
      <CommandUIDefinitions>
        <CommandUIDefinition Location="Ribbon.WikiPageTab.Share.EmailPageLink">
          <Group
          Id="Ribbon.WikiPageTab.Share"
          Sequence="30"
          Command="ShareGroup"
          Description=""
          Title="$Resources:core,cui_GrpShare;"
          Image32by32Popup="/_layouts/15/$Resources:core,Language;/images/formatmap32x32.png?rev=23" Image32by32PopupTop="-137" Image32by32PopupLeft="-103"
          Template="Ribbon.Templates.Flexible2"
          >
            <Controls Id="Ribbon.WikiPageTab.Share.Controls">
              <Button
                Id="Ribbon.WikiPageTab.Share.EmailPageLink"
                Sequence="10"
                Command="CustomEmailPageUrl"
                Image16by16="/_layouts/15/$Resources:core,Language;/images/formatmap16x16.png?rev=23" Image16by16Top="-115" Image16by16Left="-19"
                Image32by32="/_layouts/15/$Resources:core,Language;/images/formatmap32x32.png?rev=23" Image32by32Top="-137" Image32by32Left="-511"
                LabelText="$Resources:core,cui_ButEmailLink;"
                ToolTipTitle="$Resources:core,cui_ButEmailLink;"
                ToolTipDescription="$Resources:core,cui_STT_ButEmailLinkPage;"
                TemplateAlias="o1"
               />
            </Controls>
              </Group>
        </CommandUIDefinition>
      </CommandUIDefinitions>
      <CommandUIHandlers>
        <CommandUIHandler Command="CustomEmailPageUrl" CommandAction="javascript:alert('Hello, world');" />
      </CommandUIHandlers>
    </CommandUIExtension>
  </CustomAction>

Any help would be appreciated.

Rajasekar A.C